1. Field of the Invention
The present invention generally relates to a scroll compressor for use in a refrigerating system in, for example, an air conditioning apparatus or a refrigerator, and more particularly, to a so-called low-pressure scroll compressor in which the suction pressure acts on a tub of lubricating oil.
2. Description of the Prior Art
One example of a conventional compressor is illustrated in FIG. 8.
In the compressor of FIG. 8, there are provided a stator 102 and a rotor 103 of a motor inside a closed casing 101. A scroll compressor system 104 is placed above the motor and its driving shaft, namely, a crank shaft 105 is coupled to the rotor 103.
A hermetic terminal 106 for the motor is provided at the side surface of the closed casing 101. A cooling medium or coolant entering from a suction pipe 107 into the closed casing 101 is partly sucked into the compressor system 104 from a suction port 108 as indicated by a large arrow, and partly scattered in the closed casing 101 by the flow of the air inside the closed casing 101. A fixed scroll component 109 has a spiral vane 110 and a mirror plate 111. A turning orbiting scroll component 112 has a spiral vane 113 and a mirror plate 114. The spiral vanes 110 and 113 are brought in mesh with each other, so that the vanes 110 and 113 constitute a compression chamber 115 which, moving towards the center of the compressor from the outer periphery thereof to reduce its capacity, carries out compression action. The coolant coming out of an exhaust port 116 which is provided at the center of the fixed scroll component 109 is guided to an exhaust pipe 118 of the compressor from an exhaust space 117.
The pressure in the compression chamber 115 presses the turning scroll component 112 against the opposite side of the compression chamber 115, the force of which is supported by a thrust bearing 120 fixed to a bearing member 119 which supports first and second main shafts 121 and 122 of the crank shaft 105.
The first main shaft 121 has a turning driving bearing 123 provided inside thereof eccentrically from the center of the shaft. A turning driving shaft 124 fitted in the turning bearing 123 is provided in the mirror plate 114 of the turning scroll component 112.
In the outer periphery of the thrust bearing 120, a rotation restricting element 127 having a pair of keys 126 on the opposite surfaces of a circular ring member 125 is provided so as to restrict the rotation of the turning scroll component 112.
A lubricating oil tub 128 is placed in the lower part of the closed casing 101. The lubricating oil in the tub 128 is supplied from an oil feed port 129 of the crank shaft 105 to every sliding portion of the compressor by an oil feed pump 130.
In the conventional compressor having the above-described structure, the lubrication by the lubricating oil in each sliding portion of the compressor will be set up as described hereinbelow.
Upon rotation of the electric motor, the lubricating oil in the tub 128 is, as indicated by a small arrow, brought into the oil feed port 129 of the crank shaft 105 by the action of the oil feed pump 130. The lubricating oil is, passing through an oil passage 131 in the crank shaft 105 and lubricating the turning driving bearing 123 of the compression system 104 and each sliding portion in the inner periphery of the thrust bearing 120 and in the outer periphery of the first main shaft 121, then supplied to a secondary bearing 132 provided in the lower part of the bearing member 119. Thereafter, the lubricating oil is discharged to the upper part of the motor to be returned to the tub 128 through a notched part 133 formed in the outer edge of the stator 102.
However, the conventional low-pressure scroll compressor in which the suction pressure acts inside the closed casing 101 as described above has such demerits as follow.
In other words, the inside of the closed casing 101 is divided into the suction pressure space and the exhaust pressure space by the compression system 104, and therefore, the lubricating oil which is mixed with the coolant and is discharged out of the compression system 104 is never returned into the compression system until the lubricating oil moves all around the refrigerating cycle.
Meanwhile, the closed casing 101 has many sliding portions thereinside such as the compression system 104, etc., thus requring much lubrication oil.
Consequently, in the conventional low-pressure scroll compressor in which the lubricating oil is returned to the compression system after being circulated all around in the refrigeration cycle, it is disadvantageous that:
(1) if the amount of the lubricating oil to be discharged in mixture with the coolant is increased, an oil film is generated in the heat exchanger (regenerator) of the refrigerating cycle, thereby lowering the regeneration efficiency of the refrigerating cycle, and
(2) if the amount of the lubricating oil to be supplied to the compressor system 104 is reduced contrary to the above case (1), the compressor system 104 may be overheated, or the oil film may be insufficiently produced to lower the sealing efficiency, resulting in total decline of the efficiency of the compressor itself.
It has been widely practiced in recent years to control the capacity of the compressor that the rotating number of the compressor (motor) is increased or decreased depending on required efficiency, that is, a so-called inverter driving of the compressor has been widely known.
However, if the inverter driving is applied to the conventional low-pressure scroll compressor, the disadvantages (1) and (2) described earlier would be of much more concern.
In other words, although the amount of the lubricating oil necessary for the compressor system 104 is arranged to be increased in proportion to the increase of the rotating number of the motor, sufficient lubricating oil for high-speed rotation of the compressor can not be obtained in such construction because only the lubricating oil leaking from the portions sliding with the thrust bearing 120 is led to the compressor system 104.
For solving the above problem, it may be possible, for example, that the ring member 125 is made thinner or a groove or the like is formed in a part of the ring member 125, so that the lubricating oil is partly positively guided into the compression system 104. In spite of this arrangement, however, sufficient amount of the lubricating oil can not be secured for the entire range of operation from the low-speed rotation to the high-speed rotation of the motor.
The above fact could be confirmed by an experiment, the reason for which will be as follows.
Namely, since the flow of the air is given rise to in the closed casing 101 in the rotational direction of the motor, the coolant returning from the suction pipe 107 rides on the flow of the air and is sucked in from the suction port 108 to be compressed in the compressor system 104 and exhausted. At this time, the lubricating oil included in the coolant is also sucked in from the suction portion 108 without being separated sufficiently from the coolant in the suction space, then repeatedly going around the refrigerating cycle.
In the above case, when the rotating number of the motor is further increased, the amount of the lubricating oil drawn up by the oil feed pump 130 is increased too, and accordingly, the amount of the lubricating oil to be supplied becomes larger than the amount of the lubricating oil collected from the returning coolant, resulting in lack of the oil amount in the tub 128. In consequence, such inconveniences are brought about that the sliding portions may be overheated, or the regenerating efficiency may be lowered because of the increase of the lubricating oil circulating in the circuit of the coolant (not shown) outside the closed casing 101.
FIG. 7 is a characteristic diagram showing the relationship between the rotating number N (rpm) and the exhaust amount of the lubricating oil V (cc/min.) in the low-pressure scroll compressor in which the rotating number of the motor is controlled.
The foregoing description is represented by the characteristic diagram shown by a broken line.
Moreover, in the conventional low-pressure scroll compressor, the flow of the air is given rise to in the same direction as the rotating direction of the motor in the space at the side of the suction port 108, and therefore the lubricating oil included in the coolant is easier to be sucked in from the suction port 108, and is difficult to be collected. It becomes more difficult to collect the lubricating oil included in the coolant as the rotating number of the motor is increased, as has been described earlier.
Further, since the closed casing 101 is filled with the low-temperature, low-pressure coolant in the conventional low-pressure scroll compressor, the closed casing 101 is cooled, easily causing the condensation of dew in the outer periphery of the closed casing 101.
Although the dew condensation described above is able to be eliminated if the closed casing 101 is covered with an adiabatic material or in a similar manner, the hermetic terminal 106, which is a power take-in port for the motor, is hard to shut off from the heat. Particularly, since the hermetic terminal 106 is applied with electric pressure, it is considerably important to prevent leakage or short-circuiting resulting from the dew condensation.
At the high-speed rotation of the motor, the rotating number of the crank shaft 105 becomes increased, and accordingly the supply efficiency of the lubricating oil becomes large because of the increase of the centrifugal force. Therefore, the lubricating oil is discharged more into the space between the bearing member 119 and the motor. Moreover, as the speed of the coolant gas sucked in from the suction port 108 is also increased, a large amount of the lubricating oil is sucked in from the suction port 108 outside the closed casing 101 through the compressor system 104 and the exhaust pipe 118, to be returned from the suction pipe 107 again. Accordingly, the lubricating oil returning from the suction pipe 107 is mixed with the lubricating oil discharged out of the upper part of the rotor 103 after lubricating and cooling each of the bearing members and the sliding portions, and is sucked into the suction port 108. Thus, the discharging amount of the oil is increased more and more at the high-speed rotation of the motor as clearly seen from the diagram shown by the broken line in FIG. 7, and finally the lubricating oil in the tub 128 is exhausted.
Therefore, it becomes necessary, particularly in the low-pressure scroll compressor which is adapted to control the rotating number of the motor, that the amount of the lubricating oil to be supplied to the compressor system 104 is controlled within a proper range regardless of the increase or decrease of the rotating number of the motor, and simultaneously, the lubricating oil is securely collected in the tub 128.